Cathode-grid spacing means



Feb. 3, 1959 w. R. WHEELER CATHODE-GRID SPACING MEANS Filed June 14, 1957 IN VENTOR WILLIAM R. WHEELER ATTORNEY CATHODE-GRID SPACING MEANS William R. Wheeler, Wantagh, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application June 14, 1957, Serial No. 665,692 7 "Claims. Cl. 313-256) This invention relates to electron tubes with exceedingly small grid-cathode spacing.

In order to obtain high performance of electron tubes it is often necessary to make the cathode-grid spacing 0.001 to 0.003 inch. For spacings in the order of 0.001 inch it is desirable to maintain the separation with a tolerance of 0.0002 inch in order to avoid unduly large variation in tube characteristics. Normally, the gridcathode spacing is dependent on the accumulated tolerances of a number of tube parts making the maintainance of grid-cathode tolerance of .0002 inch, with prior art technique, extremely difiicult.

A method and tube structure is herein disclosed wherein such tolerance can be maintained with case.

It is an object of this invention to provide a method whereby exceedingly close spacing between two elements of an electron tube may be obtained easily.

It is a further object of the invention to provide a construction of an electron tube wherein exceedingly close spacing between grid and cathode may be obtained and held with exceedingly small variations.

It is a still further object of the invention to provide a novel support for a cathode and a surrounding heat shield.

Other objects will become apparent after reading the following specification.

In carrying out the method, grid-cathode spacing is effected by fixing in position all parts of the tube mount except the cathode and then spacing the cathode from the grid by the use of a temporary spacer between the grid and cathode, said spacer being of the desired thinness and having very smooth surfaces. The cathode is next fixed in position and thereafter the spacer is slipped out from between the spaced elements.

For a fuller understanding of the invention, attention is directed to the following specification and accompanying drawings in which:

Fig. 1 is a front elevation of a stem and tube mount in accordance with this invention.

Fig. 2 is a vertical section through the same.

Fig. 3 is a section on the line 3-3 of Fig. 2 and Fig. 4 is a perspective view of a fragmentary portion of the tube showing a portion of the spacer utilized during the manufacture of the mount.

It should be understood that the invention is here illustrated as applied to a triode. It will be obvious, as the specification is read, that other types of tubes may embody the invention, too.

in the specific embodiment here shown, the tube comprises an anode 10, a control grid 12 and an indirectly heated cathode 14. The tube is of the planer type wherein all of the electrode elements of the mount are supported either directly or indirectly by a pair of ceramic rods 16.

The anodes is a channel shaped member whose web faces the grid and cathode and whose flanges, at each end of the anode, are provided with rod securing clips 18. Each clip spans the channel at the end thereof nited States Patent ice and is welded thereto as indicated at 20, the bridge portion of the clip being formed into a loop 22 frictionally embracing a rod 16. Threaded on each rod and resting against an edge of the loop is a ceramic washer 24 and engaged against this washer is the next electrode, here shown as control grid 12. It is obvious that as many washers and electrode elements as desired may thus be stacked on the ceramic rods 16. After the last electrode, there is slipped on each of the rods a ceramic washer 26 and finally a securing clip 28. The length of the washers 24 and 26 are selected to give the desired spacing between elements as will be apparent from the following.

The cathode is supported from the ceramic rods directly or indirectly. In this instance the cathode is supported by a cathode heat shield 30 which itself is fastened to the securing clips. As shown in the several views, the heat shield 30 is in the form of a ribbed channel which obviously could be of one piece. As here shown, the channel is made of two metal pieces, preferably with a heat reflecting interior surface, the channel having two flanges 32, a web 34, and a rib 36. The channel is held to the mount by being spot welded to the clips 28, as indicated at 33. In building the tube mount, all of the parts just described are assembled as indicated except that prior to afiixing the heat shield to the securing clips 23, the cathode 14 with its internal heater 40 is inserted to lie loosely within the heat shield channel, with its emissive surface 42 directed toward the grid. The emissive surface is of a high density type with smooth surface. The grid is of the frame grid type, that is to say a flat piece of metal of molybdenum or the like having a window spanned by the grid laterals and which laterals are fastened to the grid frame on the side nearest the cathode in any suitable manner as by brazing or welding the wires to the frame.

The cathode sleeve here shown is in the form of a parallelepiped, and is provided at its upper and lower edges, at opposite corners thereof with the struts 44, these struts being bent to extend in opposite directions, parallel and adjacent to the end faces of the sleeve. Although here shown as welded to the cathode sleeve,

they could be integral parts thereof. The heat shield has formed therewith, as by cutting out portions thereof, a pair of anchor ears 46, these being located on opposite corners of the shield and in position to mate with struts 44 and preferably being wider than said struts for a purpose to be disclosed.

After the parts had been assembled as previously described, a thin strip 48 of burr free, flexible, highly polished, hard material is placed between the cathode and grid and in the space between the two washers 26. A suitable strip for this purpose can be cut from material known to the art as Mylar. This strip is selected to be of the requisite thickness, as 0.001 inch. It is put in position so that it will rest on the grid and then the cathode sleeve is located against the strip and uniformly and lightly pressed thereagainst by a jig pressing down down on the edges of the struts. The ears on the shield are wide enough to allow lateral adjustment thereacross of the ears on the cathode sleeve. The cathode support struts will then be opposite the heat shield anchor ears and are welded to them as indicated at 50.

After removal of the mount assembly from the jig, the strip is withdrawn, leaving the cathode properly spaced from the grid. The high density smooth coating on the cathode sleeve and the grid construction with laterals directed substantially in parallelism with direction of removal of the spacer, permits easy removal of the spacer without injury to the grid or flaking of the emissive material on the cathode sleeve. After the mount is thus prepared its electrodes are welded to leads 52 of a stem 54in conventional fashion.

Although the invention has been disclosed as pertaining to the spacing between grid and cathode, it is obvious that the invention is adaptable to 'eficct'spacing between other electrodes of the mount.

Having thus described the invention, what is claimed as new is:

1. An electrode assembly comprising a pair of parallel, spaced, insulated, support rods, electrodes spanning the rods with the rods passing through apertures in ends of said electrodes, an additional support element having at least one clip surrounding each rod, said support element also having an ear, insulating spacers between the electrodes and between the additional support element and adjacent electrode, and an additional electrode having at least one strut secured to the ear of said additional support element by said strut.

2. An electrode assembly comprising a pair of spaced,

parallel, insulated support rods, an anode and a grid mounted in spaced relationship to each other on said support rods, a cathode heat shield also mounted on said support rods and in spaced relationship to the grid, said heat shield having cathode support ears and a cathode having struts registering with said ears and fastened thereto,

3. An electrode assembly comprising a pair of spaced, parallel, insulated, support rods, an anode and a grid mounted in spaced relationship to eachother onsaid support rods, a cathode heat shield also mounted on said support rods and in spaced relationship to the grid, said heat shield comprising a channel, a cathode within said channel, ears on said channel at opposite corners thereof, said cathode having struts overlying the ears and fastened thereto.

4. An electrode assembly comprising parallel, spaced, insulating rods, an anode spanning said rods and fastened in position thereon, a grid spanning said rods, a cathode support means supported by said rods and fastened thereto, independent insulating spacing washers on said rods between said anode and grid and between the grid and cathode support means, cathode mounting means having an extent in a direction parallel to the rods on said cathode support means, a cathode parallel to the fastened to the cathode mounting means.

5. An electrode assembly comprising a pair of parallel, spaced, insulating rods, an'anode spanning said rods and fastened in position on said rods, a grid spanning said rods, a cathode support element also spanning said rods and fastened thereto, independent insulating spacing Washerson said rods between said anode and grid and between the grid and cathode support element, cathode mounting means having an extent in a direction parallel to the rods onfsaid cathode supportelernent, a cathode parallel to the grid and spanning the rods, and means on the cathode fastened to the cathode mounting means on the cathode support element.

6. An electrode assembly comprising parallel, spaced,

insulating support rods, an anode spanning said support rods and secured thereto, a grid spanning said support rods and supported thereby, insulating washers on said support rods filling the space between said anode and said grid, a channel member, having flanges and a web, spanning said support rods and secured thereto, the flanges being directed toward the grid, other insulating washers on said support rods between saidgrid and channel member and maintaining them in spaced relationship, a cathode between the flanges of the channel member, ears on said flanges atopposite corners of the channel member and extending laterally in opposite directions from said channel member parallel to the ends thereof, and struts on said cathode registering with said ears and fastened thereto.

7; A method for manufacturing an electron tube mount having at least an anode, a grid and a cathode, said method comprising fixedly mounting all of said electrodes save the cathode on a support, fixedly mounting a cathode support element with the cathode associated th'erewith but unattached thereto on said first support, in-

serting a spacer element between the grid and cathode, pressing the cathode against the spacer element and while so pressed attaching the cathode to the cathode support element, and withdrawing the spacer element from between the grid and cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,747,120 Price May 22, 1956 

